Mithraism, one of the major religions of the Roman Empire, the cult of Mithra, the ancient Persian god of light and wisdom.... It was a rival to Christianity in the Roman world.

Mithraism was similar to Christianity in many respects, for example, in the ideals of humility and brotherly love, baptism, the rite of communion, the use of holy water, the adoration of the shepherds at Mithra's birth, the adoption of Sundays and of December 25 (Mithra's birthday) as holy days, and the belief in the immortality of the soul, the last judgment, and the resurrection. Mithraism differed from Christianity in the exclusion of women from its ceremonies and in its willingness to compromise with polytheism. The similarities, however, made possible the easy conversion of its followers to Christian doctrine.